Ductile,weldable high-strength-steel wire and method for producing same

ABSTRACT

A DUCTIBLE, WELDABLE, HIGH-STRENGTH STEEL WIRE CONTAINING 0.12 TO 0.30% C, 0.30 TO 1.60% MN, AND 0.005 TO 0.003% B, BALANCE FE IS PRODUCED BY EMPLOYING COLD REDUCTIONS OF FROM ABOUT 1 TO 60%, AUSTENITIZING WITH THE RANGE A3 TO 1900*F., AND THEN QUENCHING IN OIL. THE PROCESSING VARIABLES EMPLOYED ARE BALANCED WITH THE COMPOSITION AND THE FINAL DIAMETER OF THE WIRE IN ACCORD WITH TWO EQUATIONS, TO ACHIEVE A SUPERIOR COMBINATION OF HIGH STRENGTH AND DUCTILITY.

United States Patent 3,834,948 DUCTILE, WELDABLE HIGH-STRENGTH-STEEL WIRE AND METHOD FOR PRODUCING SAME Kenneth G. Brickner, OHara Township, Allegheny County, and Edward B. Stanley, Washington Township, Westrnorelaud County, Pa., assignors to United States Steel Corporation No Drawing. Filed Oct. 13, 1971, Ser. No. 189,003 Int. Cl. C21d l/58, 7/02, 9/52 US. Cl. 1482 4 Claims ABSTRACT OF THE DISCLOSURE A ductile, weldable, high-strength steel 'wire containing 0.12 to 0.30% C, 0.30 to 1.60% Mn, and 0.0005 to 0.003% B, balance Fe is produced by employing cold reductions of from about 1 to 60%, austenitizing with the range A to 1900 F., and then quenching in oil. The processing variables employed are balanced with the composition and the final diameter of the wire in accord with two equations, to achieve a superior combination of high strength and ductility.

This invention relates to a ductile, weldable highstrength steel wire and to a method for the production of such wire. The invention is more specifically directed to a method for the production of steel wires in diameters of up to about 4 inch, that exhibit tensile strengths and ductilities equal to or superior to that of conventional hard drawn Class I spring wires, and that are suitable for use in the production of wire products requiring Weldability and formability far superior to that of such conventional wire.

High-strength steel wires are employed for a variety of fabricated items such as springs, rake tines, snap ties, screens, etc. A great many of these items require a combination of high-strength (greater than 180 k.s.i.) and high ductility (greater than 40 percent reduction in area) so that they may be formed cold, over small radii. In order to achieve such high strengths it has been necessary to employ carbon contents in excess of about 0.45 percent. Unfortunately, such conventional hard drawn wires are not readily weldable because of the high carbon content required to obtain the desired strength level. Therefore, in order to obtain a satisfactory welded product (i.e. elimination of weld embrittlement), it has been necessary to resort to elaborate preheating and/or postheating techniques. Satisfactory weldability could be achieved by employing carbon contents below about 0.30 percent, but heretofore, the consistent achievement of strengths in excess of 180 k.s.i., coupled with reductions in area of greater than 50%., in such low carbon steels has alluded the art, especially for larger diameter wires (e.g. greater than 0.2 inches diameter). Alloy additions which eifect an increase in strength and hardenability generally cause a concomitant decrease in ductility. On the other hand, heat-treatments such as tempering or annealing, which provide an increase in ductility, result in an accompanying decrease in strength level.

It is therefore an object of this invention to provide a method for producing a low carbon, weldable steel with a minimum tensile strength of 180 k.s.i. and a minimum reduction of area of 50 percent.

It is another object of this invention to provide a method of tailoring the C, Mn and B content of a steel, to certain specific processing parameters so that a weldable, ductile, high strength steel wire may be produced.

It is another object of this invention to provide a method for tailoring the processing variables to a steel with a preferred carbon content of from 0.15 to 0.25 percent, to achieve a tensile strength in excess of 200 }:s.i. in

3,834,948 Patented Sept. 10, 1974 combination with reduction-of-area ductility in excess of 50 percent.

It is a further object of this invention to achieve the above stated levels of strength and ductility in wire products ranging from about 0.10 to 0.75 inches in diameter.

These and other objects and advantages of the invention will be more apparent 'when read in conjunction with the appended claims and the following description.

Twenty-eight 300-pound laboratory induction furnace heats were melted, cast into ingots, and converted into hot-rolled rod. The rod samples were pointed, cleaned, and cold-drawn to various degrees of reduction. Specimens were then austenitized for 20 minutes at specified temperatures prior to quenching in agitated oil. The tensile properties were then determined and compared with the compositions and processing parameters for each of the specimens. It was found that the strength and ductility achieved, could be expressed by the following equations:

(I) Tensile Strength, (k.s.i.)=+l25.03+355.74

(percent C.)+53.l0 (percent Mn)+7987 (percent B)=0.18 (percent Cold Reduct.)-+229242 (percent C) (percent B)+6402 (percent Mn) (percent B) -|284.26 Diam., inches) --303.98 (Diam., inches) 0.0444 (Austenitizing Temp. F.)80479 (percent B) (Diam., inches) (II) Reduction of Area, percent=+24.27+l00.60

(percent Mn)+0.l72 (percent Cold Reduction) +0.0504 (Austen. Temp., F.)+l.l10 (percent Cold Reduction)(Diam., inches)ll4.37 (percent C)2l89 (percent B)-l4.57 (Diam., inches) 24617 (percent C)(percent B)3.51 (percent C) (percent Cold Reduction)-0.0656 (percent Mn) (Austen. Ternp., F.)

With the aid of these equations, it is therefore possible to determine the compositional and processing variables which will meet the objects of this invention, i.e. provide a combination of high strength 180 k.s.i.) and good ductility 50 percent reduction in area). The compositional and processing variations to which the above equations are applicable, should be selected from the following ranges:

Carbon, percent-0.l2 to 0.30

Manganese, percent-0.30 to 1.60

Boron, percent-0.0005 to 0.003 with balance Fe and incidental steelmaking impurities Wire Drawing Reduction, percent--1 to 60% Austenitizing Temp, F.A to 1900 F. followed by an oil quench Referring to the equations, the various factors (and their relative importance) which affect both tensile strength and reduction of area may be delineated. Thus, for example, it may be seen that in addition to the well known effects of C and wire diameter on strength, both the tensile strength and the ductility may be simultaneously increased by proper selection of austenitization temperature and cold reduction. The salient information 'which can be derived from these equations is first summarized and then discussed more fully below.

Tensile Strength increases with increasing amounts of C, Mn and B; increases as wire diameter is decreased;

increases as the amount of cold reduction is increased; decreases as the austenitization temperature is increased.

Reduction of Area decreases as C and B are increased; increases as Mn is increased;

not significantly affected by wire diameter when the amount of cold reduction is small, but increases significantly as wire diameter is increased for wire which has received a large amount of cold reduction;

increases as the austenitizing temperature is increased,

when Mn is on the low end of the range;

decreases as the austenitizing temperature is increased,

with Mn on the high end of the range;

both increases or decreases as cold reduction is increased (depending on final wire diameter and C content).

Thus, in addition to certain well known effects (e.g. the effect of C, Mn, and B on tensile strength), it may be seen that some unexpected factors also play a signi-fi cant role in their effect on tensile strength and especially in their effect on ductility. For example, the marked effect of cold reduction on the properties of a subsequently heat-treated wire, and the interrelationship between cold reduction, carbon content and wire diameter should be noted. This effect of prior cold work is surprising since heretofore it was believed that any such effects would be washed out by a subsequent austenitizing heat treatment. Such prior cold work, in addition to effecting an increase in tensile strength, will in certain instances have a marked eifect on ductility. Examples of these instances and their applicability to the production of three different wire diameters are presented below:

0.65-inch-diameter wire.--For wire of this diameter, made from teels with less than about 0.20% C, the reduction-of-area ductility can be significantly improved by increasing the amount of cold drawing before austenitization. Therefore, when such lower carbon contents are contemplated, rod with significantly larger diameters should be employed as the starting material, so that the final diameter wire will have been given high amounts (preferably greater than 40%) of cold drawing.

If about 0.25% C is to be employed in the composition of the steel, the reduction of area ductility is not significantly affected by the amount of cold reduction. Therefore, to achieve a desired strength and a high ductility in excess of 50% reduction-in-area, it will be neces sary to employ one or more of the other above enumerated factors, e.g. high manganese, low austenitization temperature, low B.

For 0.65-inch-diameter wire with carbon contents approaching 0.30 percent, the ductility decreases with increasing amounts of cold reduction before austenitization. Therefore the rod diameter employed for making wire of this diameter should be as close as is practical to the final wire diameter.

0.45-inch-diameter wire-The ductility of wire of this diameter, made from 0.15% C steel can also be significantly enhanced by employing large amounts of cold reduction. At about 0.20% C, the amount of cold reduction becomes less significant. Therefore, 0.20% C wire of this diameter can be made from various diameter rods without impairment of ductility. However, if carbon contents of 0.25% or 0.30% are contemplated, the amount of cold reduction should be kept as small as is practicable, since the ductility will be decreased significantly with increasing amounts of cold drawing.

0.25-inch-diameter-wire.Here, with carbon contents of about 0.15 to 0.20 percent the reduction-of-area ductility decreases (but less significantly than with larger diameter wires) as the amount of cold drawing increases; with the degree of impairment of ductility increasing as the carbon content is increased. Therefore, to prevent impairment of ductility the rod diameter en ployed should preferably be similar to the desired diameter of the wire, especially when carbon contents in excess of 0.25% are employed.

The discussion above was directed to the attainment of weldable wire with certain desired strength levels, i.e. those which are equivalent to conventional hard-drawn Class I spring wires. However, in many cases, even higher strength levels at equivalent ductilities' (greater than 50% reduction-in-area) are desirable. Such higher than normal strength, if accompanied by high ductility, will increase the service life and performance of the product or will permit a decrease in the size and weight of the equipment components (or an increase in payload), and thereby further .reduce overall costs. It is therefore a preferred embodiment of this invention to utilize the above equations for the production of low carbon, low alloy wire which exhibits a tensile strength in excess of 200 k.s.i. in combination with a reduction-of-area in excess of 50%. Such high strength wire will not only provide greater service life but the accompanying high ductility will permit its application in a wider range of products, i.e. in products requiring crimps or very small radii bends, and in which only relatively low strength wires were heretofore employed.

The method of this invention was employed for the production of welded football face masks. Such masks are now extensively employed in both college and professional games and are generally made from relatively low strength A181 1017 wire, because of the requirement for high ductility and weldability of the wire. These masks generally need to be replaced after about two football games because of their low strength.

A 0.22 percent carbon steel was processed, within the scope of this invention, into 0.192-inch-diameter wire. The resultant product had a Tensile Strength of 215.8 k.s.i. and a Reduction of Area of 59.2 percent. The wire was formed into football face masks and welded without difliculty. These masks were used in three professional football games and then examined for signs of failure. No damage was noted, indicative of both the high strength of the wire and the integrity of the welds.

We claim:

1. A method for the production of a weldable steel wire product exhibiting a superior combination of high strength and good ductility as evidenced by an ultimate tensile in excess of k.s.i. and a reduction of area in excess of 50%, which comprises,

a. adjusting a steel melt to provide a rod composition within the range consisting of, in weight percent;

C 0.12 to 0.30 Mn 0.30 to 1.60 B 0.0005 to 0.003 balance Fe and incidental steelmaking impurities,

b. cold reducing said rod to a wire of desired diameter,

c. heating said wire to a temperature above the A and below 1900 F. for a time sufiicient to effect the substantially complete austenitization thereof, and then,

d. quenching said wire in oil to produce a substantially martensite microstructure; wherein the adjustment of said composition, said cold reduction and said heating are conducted in accord with the following equations;

For Tensile Strength +355.74(percent C) +53.l0(percent Mn) +7987 (percent B) +0.18( percent Cold Reduction) +299242(percent C) (percent B) +6402(percent Mn) (percent B) +284.26(Diam., inches) 303.98 (Diam., inches) 0.0444(Austenitizing Temp. F.)80479(per B)(Diam., inches) 254.97 and For Reduction of Area +100.60(percent Mn) +0. 172 (percent Cold Reduction) +0.0504(Austen. Temp. F.) 1.110(percent Cold Reduction) (Diam., inches) 1 14.37(percent C) 2l89(percent B) -14.57(Diam., inches) -24617(percent C) (percent B) 3.5 1 (percent C) (percent Cold Reduction) 0.0656(percent Mn) (Austen.

Temp. F.)z25.73

2. The method of claim 1 wherein said carbon content is within the range 0.15 to 0.25 percent.

3. The method of claim 2, wherein said composition, said cold reduction and said heating are selected so that the sum of the termsdn equation I are 274.97, so as to produce a wire with a tensile strength in excess of 200 k.s.i. v

4. The method of claim 3, wherein said wire diameter is within the range of about 0.10 to 0.75 inches.

References Cited UNITED STATES PATENTS 3,532,560 10/1970 Tomio lta ct al. 14s-12x 2,527,731 10/1950 Ilacqua et a1 75-123 B 3,666,572 5/1912 Nakagawa et al. 148-12 x CHARLES N. LOVELL, Priznary Examiner US. Cl. X.R.

UNITED STATES PATENT OFFICE ,7 CERTIFICATE OF CORRECTION Patent No. 3,834,948 Dated Septemberv 1O 1974 1 Kenneth G. Brickner et a1. Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 21, "B)=O.18" should read B)+O.18

line 21, "+229242" should read #299242 line '23, "+284.26 Di am., in c hes) should read +284.26(Diam., inches) Column 4, line 64, "-80479(p er B)" should read I =80479(percent B) Signed and sealed this 3rd day of December 1974,.

(SEAL) Attest:

McCOY M. GIBSON JR. c. MARSHALL DANN Attesting Officer Commissioner of Patents USCOMM-DC 60376-P69 u.s. GOVERNMENT PRINTING OFFICE: 859 93 O 

